Method for manufacturing float glass and apparatus for manufacturing the same

ABSTRACT

The present invention provides a method for manufacturing a float glass by floating the glass on a molten tin that is contained in a molten tin bath, which includes the steps of a) discharging a portion of the molten tin in the molten tin bath to the outside of the molten tin bath; b) removing oxygen dissolved in the molten tin that is discharged from the molten tin bath by injecting an oxygen stripping gas that contains hydrogen into the molten tin; and c) returning the molten tin from which oxygen is removed to the molten tin bath, and an apparatus for manufacturing the same.

This application is a divisional application of U.S. patent applicationSer. No. 12/677,073, filed on Mar. 8, 2010, which is a national stageapplication of International Application No. PCT/KR2009/005658, filedOct. 1, 2009, which claims priority to Korean Application No.2008-0097373, filed Oct. 2, 2008, all of which are hereby incorporatedby reference for all purposes as if fully set forth herein in theirentireties.

TECHNICAL FIELD

The present invention relates to a method for manufacturing a floatglass by floating glass on a molten tin included in a molten tin bath inwhich a dissolved oxygen amount in the molten tin bath can be reduced,and an apparatus for manufacturing the same.

BACKGROUND ART

A float glass is manufactured by using a typical float process. That is,by introducing the molten glass to an upper portion of molten tin thathas the large specific gravity and is included in the molten tin bath touse a float process that manufactures a panel glass having nounevenness, it is manufactured.

However, when the panel glass is manufactured by using the molten tinbath, there is a large technical problem in a known manufacturingprocess in that there is a bottom open seed due to oxides of tin oroxygen dissolved in tin.

Therefore, in order to solve this, a technology in which an atmosphereof the molten tin bath is maintained under an atmosphere having nooxygen, and sealing is carried out so as to prevent inflow of air andconsequently to prevent oxygen from being dissolved in tin has beendeveloped. However, since this is not suitable to sufficiently removeoxygen that is dissolved in tin, there is a difficulty in reduction ofproduct defect ratios.

DISCLOSURE Technical Problem

It is an object of the present invention to provide a method formanufacturing a float glass by efficiently removing oxygen in the moltentin by an oxygen solubility difference according to temperature and anoxygen stripping gas including hydrogen with respect to a dissolvedoxygen amount of a molten tin in a molten tin bath, such that productdefects can be reduced, and an apparatus for manufacturing the same.

Technical Solution

The present invention provides a method for manufacturing a float glassby floating the glass on a molten tin that is contained in a molten tinbath, which includes the steps of a) discharging a portion of the moltentin in the molten tin bath to the outside of the molten tin bath; b)removing oxygen dissolved in the molten tin that is discharged from themolten tin bath by injecting such an oxygen stripping gas as hydrogeninto the molten tin; and c) returning the molten tin from which oxygenis removed to the molten tin bath.

The present invention provides an apparatus for manufacturing a floatglass by floating the glass on a molten tin that is contained in amolten tin bath, the apparatus comprising: a molten tin bath; adischarge line that is connected to an inside of the molten tin bath,and discharges a portion of the molten tin in the molten tin bath to theoutside of the molten tin bath; an oxygen stripping chamber that isconnected to the discharge line and receives the molten tin dischargedfrom the molten tin bath through the discharge line; an injection devicethat is provided in the oxygen stripping chamber and injects the oxygenstripping gas including hydrogen to the molten tin in the oxygenstripping chamber; and a returning line that returns the molten tin fromwhich oxygen is removed by the injection device to the molten tin bath.

Advantageous Effects

According to the present invention, a dissolved oxygen amount in amolten tin bath can be reduced. Therefore, such tin oxide-relateddefects as Tin Drop, Tin Pick-up and Top Speck, and Bottom open seed canbe minimized.

DESCRIPTION OF DRAWINGS

FIG. 1 is a plan view of a molten tin bath according to the presentinvention;

FIG. 2 is a cross-sectional view of an oxygen stripping chamber and aheating chamber taken along the line A-A of FIG. 1; and

FIG. 3 is a cross-sectional view of a porous membrane of FIG. 2.

BEST MODE

The present invention provides a method for manufacturing a float glassby floating the glass on a molten tin that is contained in a molten tinbath, which includes the steps of a) discharging a portion of the moltentin in the molten tin bath to the outside of the molten tin bath; b)removing oxygen dissolved in the molten tin that is discharged from themolten tin bath by injecting an oxygen stripping gas that containshydrogen into the molten tin; and c) returning the molten tin from whichoxygen is removed to the molten tin bath.

In the present invention, oxygen in the molten tin can be efficientlyremoved without an affection on manufacturing of the float glass in themolten tin bath by not directly performing a process for removing oxygenin the molten tin in the molten tin bath for manufacturing the floatglass but performing the process at the outside of the molten tin bath.

In addition, the present invention is characterized in that it uses theoxygen stripping gas when oxygen is removed in the molten tin andsimultaneously, uses a method for injecting oxygen stripping gas intothe molten tin, not a method for simply contacting the oxygen strippinggas with the surface of the molten tin. As described above, theinjection of the oxygen stripping gas into the molten tin may be moreefficiently carried out by performing the removal of oxygen at theoutside of the molten tin bath. That is, in the case of when the removalof oxygen is directly carried out in the molten tin bath, as describedabove, if the oxygen stripping gas is injected into the molten tin, itmay affect the manufacturing of the float glass.

In the present invention, the oxygen stripping gas is not simplycontacted with the surface of the molten tin, but oxygen may be moreefficiently removed by directly injecting oxygen stripping gas into themolten tin. In more detail, in the case of when the oxygen stripping gasis simply contacted with the surface of the molten tin, since thecontact surface between the oxygen stripping gas and the molten tin issmall and the oxygen stripping gas is reacted with oxygen that iscapable of being present under the atmosphere contacting with the moltentin before oxygen in the molten tin is removed, the oxygen removingefficiency is reduced. Accordingly, in the method according to thepresent invention, oxygen may be more efficiently removed as compared toa technology for simply contacting the oxygen stripping gas with themolten tin.

In the step a), the zone of the molten tin bath from which the moltentin is discharged is not limited, but in the zone at which thetemperature of the molten tin is in the range of 700 to 1000° C. amongthe entire zone of the molten tin bath, the molten tin in the molten tinbath may be discharged. For example, in the cold zone of the molten tinbath at which the temperature of the molten tin in the molten tin bathis in the range of 600 to 800° C., the molten tin may be discharged.However, it is not limited thereto.

In the steps b), the oxygen stripping gas may have a flow rate in therange of 0.2 to 2 Nm³/hr, a pressure in the range of 2 to 5 kgf/cm², anda temperature in the range of 300 to 500° C. Herein, the flow rate andthe pressure are values that are set on the basis of the amount requiredin the reaction and the reference capable of passing through the porouslayer, and at the above temperature, it is possible to prevent excessivecooling of the molten tin. However, it is not limited to the above flowrate, pressure and temperature conditions, and if necessary, it may bevariously changed.

In the step b), the oxygen stripping gas may further include an inertgas. As the inert gas, nitrogen may be used. However, it is not limitedthereto.

In the case of when pure hydrogen gas is used, hydrogen may be dissolvedinto the molten tin, and if the oxygen stripping gas including the inertgas in conjunction with the hydrogen gas (H₂) is used, it is possible toprevent the dissolving of the hydrogen gas into the molten tin. Herein,the inert gas may be discharged to the discharge outlet.

In the oxygen stripping gas of the step b), the mixing ratio of theinert gas and the hydrogen gas may be 90 or more and less than 100:morethan 0 and 10 or less on the basis of the volume. Herein, in the case ofwhen the inert gas is the nitrogen gas, the ratio of the nitrogengas:hydrogen gas may be 90 or more and less than 100:more than 0 and 10or less. Meanwhile, on the basis of the volume, the ratio of nitrogengas:hydrogen gas may be 90 to 100:0 to 10.

In the step b), oxygen dissolved in the molten tin and hydrogen arechemically reacted to produce water (H₂O). Thus, oxygen that is includedin the molten tin may be removed.

In addition, by lowering the temperature of the molten tin by the oxygenstripping gas having the relatively low temperature, the saturationsolubility of oxygen that is included in the molten tin is reduced, suchthat a physical effect of extracting the dissolved oxygen is alsogenerated.

When the oxygen stripping gas is contacted with the molten tin, in thecase of when the oxygen stripping gas is bubbled, the extraction of thedissolved oxygen becomes more easy by the bubbling of the oxygenstripping gas. In detail, the bubbles of the oxygen stripping gasgenerated by the bubbling absorb oxygen dissolved in the molten tin torise. As described above, the contact area with the molten tin may beincreased by the bubbled oxygen stripping gas, such that the chemicalremoval of the dissolved oxygen in the molten tin can be moreefficiently performed. That is, since water (H₂O) is generated by thereaction between oxygen in the molten tin and hydrogen, the removal ofthe dissolved oxygen can be more efficiently performed. Furthermore, thesaturation solubility of the dissolved oxygen may be reduced by thecooling effect by the oxygen stripping gas, such that a physicalfunction capable of extracting the dissolved oxygen may be moreefficiently performed.

In the step b), the temperature of the bubbled molten tin may be in therange of 400 to 700° C.

In the step b), the reduced saturation solubility of oxygen may be tensppm or less.

The saturation solubility of oxygen dissolved in the molten tin isdescribed in the following Table 1.

TABLE 1 Tc (° C.) Solubility (%, O₂) 536 6 × 10⁻⁶ 600 2 × 10⁻⁴ 700 6 ×10⁻⁴

Herein, the solubility means the maximum oxygen saturation afterbubbling which is the solubility (thermodynamic data) according to thetemperature.

In the step c), after the molten tin from which oxygen is removed isheated, it may be returned to the molten tin bath.

The temperature of the heated molten tin may be in the range of 1200 to1400° C. If the temperature is not sufficiently high, the operationstability of the return zone of the molten tin at which glass shapingstarts may be reduced.

In the step c), the molten tin from which oxygen is removed may bereturned into the zone at which the temperature of the molten tin is inthe range of 1200 to 1400° C. of the entire zone of the molten tin bath.

The present invention provides an apparatus for manufacturing a floatglass by floating the glass on a molten tin that is contained in amolten tin bath, the apparatus comprising: a molten tin bath; adischarge line that is connected to an inside of the molten tin bath,and discharges a portion of the molten tin in the molten tin bath to theoutside of the molten tin bath; an oxygen stripping chamber that isconnected to the discharge line and receives the molten tin dischargedfrom the molten tin bath through the discharge line; an injection devicethat is provided in the oxygen stripping chamber and injects the oxygenstripping gas including hydrogen to the molten tin in the oxygenstripping chamber; and a returning line that returns the molten tin fromwhich oxygen is removed by the injection device to the molten tin bath.

The discharge line may be connected with the zone at which thetemperature of the molten tin is in the range of 700 to 1000° C. of theentire zone of the molten tin bath.

In order to lower the saturation solubility of oxygen dissolved in themolten tin by lowering the temperature of the molten tin in the oxygenstripping chamber so that oxygen dissolved in the molten tin is removed,the injection device may be a bubbling device that bubbles the oxygenstripping gas including hydrogen to the molten tin included in theoxygen stripping chamber.

The bubbling device may provide the oxygen stripping gas having a flowrate in the range of 0.2 to 2 Nm³/hr, a pressure in the range of 2 to 5kgf/cm², and a temperature in the range of 300 to 500° C.

The oxygen stripping gas may further include an inert gas. As the inertgas, nitrogen may be used. However, it is not limited thereto.

The mixing ratio of the inert gas and the hydrogen gas may be 90 or moreand less than 100:more than 0 and 10 or less on the basis of the volume.Herein, in the case of when the inert gas is the nitrogen gas, the ratioof the nitrogen gas:hydrogen gas may be 90 or more and less than100:more than 0 and 10 or less. Meanwhile, on the basis of the volume,the ratio of nitrogen gas:hydrogen gas may be 90 to 100:0 to 10.

The bubbling device may include a porous membrane and the porousmembrane may be made of a ceramic material.

The hole of the porous membrane may be formed in a direction that isvertical in respects to a flat surface, and inclinedly formed in aunidirection (see FIG. 3).

If the hole of the porous membrane is inclinedly formed in a inclinedline direction, since a rising locus of the bubbling oxygen strippinggas that passes through this may be longer than that in the case of thehole that is formed in a vertical direction, a rising path in the moltentin, that is, a reaction time of the bubbling oxygen stripping gas mayincrease.

In addition, by forming a flow capable of collecting the tin oxiderising to the surface of the molten tin to one portion, in the case ofwhen the removal of the tin oxide finally rising is required, the tinoxide rising layer may be easily removed.

It may further include a gas supply line that is connected to the oxygenstripping chamber and supplies the oxygen stripping gas bubbled by thebubbling device into the oxygen stripping chamber.

The temperature of the molten tin in the oxygen stripping chamber, whichis bubbled by the bubbling device, may be in the range of 400 to 700° C.

The saturation solubility of oxygen that is included in molten tinbubbled by the bubbling device may be tens ppm or less.

In the oxygen stripping chamber, oxygen dissolved in the molten tin andhydrogen are reacted to produce water (H₂O). Thus, oxygen that isincluded in the molten tin may be removed.

In the oxygen stripping chamber, a discharge outlet may be provided,through which water (H₂O) is discharged in a steam form to the outsideof the oxygen stripping chamber.

The apparatus for manufacturing the float glass according to the presentinvention may further include a heating chamber including a heatingdevice that is connected to the oxygen stripping chamber and heats themolten tin from which oxygen is removed in the oxygen stripping chamber.

In this case, the returning line may be provided to connect the heatingchamber and the molten tin bath, and the molten tin heated in theheating chamber may be returned to the molten tin bath.

The temperature of the molten tin that is heated in the heating chambermay be in the range of 1200 to 1400° C.

The heating chamber and the oxygen stripping chamber may be separatelyprovided and connected to each other. In addition, the heating chamberand the oxygen stripping chamber may be formed as an integrated body andthe heating chamber and the oxygen stripping chamber may be divided by apartition.

In the partition, a through hole may be formed so that the molten tinfrom which oxygen is removed in the oxygen stripping chamber moves tothe heating chamber.

The through hole may be formed in the partition so as to be disposed ata position that is lower than a liquid level of the molten tin includedin the oxygen stripping chamber. It is preferable that the through holeis formed at a position where it is immersed in the molten tin.

Since the molten tin is bubbled in the oxygen stripping chamber, thetemperature of the molten tin is lowered. Accordingly, tin oxide isgenerated on the surface and may rise. It is preferable that the throughholes is lower than the liquid level of the molten tin, for example, thethrough hole is formed at a position where it is immersed in the moltentin, in order to prevent the rising tin oxide layer from moving to theheating chamber through the through hole.

For example, the through hole may be formed in the partition so as to bedisposed at a predetermined height above the bottom surface of thechamber.

The returning line may return the molten tin from which oxygen isremoved into the zone at which the temperature of the molten tin is inthe range of 1200 to 1400° C. of the entire zone of the molten tin bath.

As described above, according to the method and the apparatus of thepresent invention, by using the method in which the oxygen stripping gasis injected to the molten tin to directly contact with tin, dissolvedoxygen may be removed by the chemical reaction where water (H₂O) isgenerated by the reaction of oxygen in the molten tin and hydrogen, anddissolved oxygen in the molten tin may be discharged by a difference insolubility due to the oxygen stripping gas having the relatively lowtemperature. Therefore, a physical function in which dissolved oxygenamount in the molten tin bath is lowered occurs.

In particular, when the oxygen stripping gas is contacted with themolten tin, in the case of using the method for bubbling the oxygenstripping gas, the extraction of the dissolved oxygen becomes easier bythe bubbling of the oxygen stripping gas. In detail, the bubbles of theoxygen stripping gas generated by the bubbling absorb oxygen dissolvedin the molten tin to rise. As described above, since the contact area ofthe bubbled oxygen stripping gas and molten tin is increased, thechemical removal of dissolved oxygen in the molten tin, that is, theremoval of oxygen according to th generation of water (H₂O) by thereaction between oxygen in the molten tin and hydrogen may be moreefficiently performed. In addition, a physical function of extractingdissolved oxygen by lowering the degree of saturation of dissolvedoxygen by the cooling effect by the oxygen stripping gas may be moreefficiently performed.

Hereinafter, the present invention will be described in detail withreference to the accompanying drawings.

In order to remove oxygen that is dissolved in the molten tin in themolten tin bath, a stripping chamber that includes the oxygen strippingchamber and a heating chamber is provided on both sides of the moltentin bath of FIG. 1. In FIG. 1, two stripping chambers arecorrespondingly provided on both sides of the molten tin bath, but thenumber and the position of stripping chambers are not limited as shownin the drawing.

The molten tin inflow side of each stripping chamber is connected to thedischarge line that supplies molten tin discharged from the molten tinbath to the inside of the oxygen stripping chamber.

The molten tin outflow side of each stripping chamber is connected tothe returning line that connects the heating chamber that heats themolten tin from which oxygen is removed in the oxygen stripping chamberin an amount of a predetermined level or less, for example, several ppmor less of dissolved oxygen, and the molten tin bath.

The stripping chamber of FIG. 2 is a chamber that includes the oxygenstripping chamber and the heating chamber as an integrated body, andincludes a partition, an oxygen stripping chamber and a heating chamberin which the oxygen stripping chamber and the heating chamber aredivided by the partition.

The partition functions to separate the atmosphere of the oxygenstripping chamber and the atmosphere of the heating chamber so as toseparate the atmosphere condition useful for oxygen removal and theatmosphere condition for suppressing reoxidation in the heating processof the molten tin from which oxygen is removed.

In the partition, the through hole through which molten tin from whichoxygen is removed in the oxygen stripping chamber moves to the heatingchamber is formed.

It is preferable that the through hole is formed in the partition so asto be disposed at a position that is lower than a liquid level of themolten tin included in the oxygen stripping chamber. As shown in FIG. 2,it is preferable that the through hole is formed at a position where itis immersed in the molten tin.

The oxygen stripping chamber is a zone that removes oxygen dissolved inmolten tin discharged from the molten tin bath.

To one side of the oxygen stripping chamber, the discharge line thatconnects the molten tin bath and the oxygen stripping chamber isconnected.

Herein, the position of the discharge line is not limited as long as itdoes not obstruct a flow of molten tin in the molten tin bath.

In the oxygen stripping chamber, a bubbling device that is capable ofblowing the mixture gas of nitrogen (N₂) and hydrogen (H₂), that is, theoxygen stripping gas, into the oxygen stripping chamber is provided. Inaddition, a gas supply line (not shown) that supplies the mixture gasinto the oxygen stripping chamber is provided so as to allow the mixturegas to pass through the bubbling device.

As long as the bubbling device is a porous membrane that has mechanicaland chemical durability in respects to molten tin, it may be variouslyused.

For example, the porous membrane may be a porous ceramic plate that hasa plurality of holes. Therefore, the mixture gas of nitrogen (N₂) andhydrogen (H₂) that is supplied to the inside of the oxygen strippingchamber passes through the hole of the porous ceramic plate.

The hole of the porous membrane, as shown in FIG. 3, may be formedinclinedly in an inclined line direction.

As described above, dissolved oxygen in the molten tin included in theoxygen stripping chamber can be chemically removed by the mixture gas ofnitrogen (N₂) and hydrogen (H₂) that is bubbled by the bubbling device,that is, dissolved oxygen can be removed according to the generation ofwater (H₂O) by the reaction of oxygen in the molten tin and hydrogen,and there are performed physical functions in which dissolved oxygen isextracted by lowering the degree of saturation of dissolved oxygen bythe cooling effect by the mixture gas introduced into the oxygenstripping chamber.

Water (H₂O) that is generated by the above process is converted intosteam in an oxygen removing zone of the oxygen stripping chamber anddischarged through the discharge outlet provided on the upper side ofthe oxygen stripping chamber.

The heating chamber is a heating zone heating molten tin that passedthrough the oxygen stripping chamber at a predetermined temperature ormore, for example, 1200 to 1400° C. or more in order to adjust thetemperature of molten tin from which oxygen is removed in the oxygenstripping chamber and the temperature of molten tin in the molten tinbath where glass is shaped.

In the heating chamber, a plurality of electric heaters are provided inorder to heat molten tin.

Herein, the electric heater may be the same or similar electric heaterin respects to the electric heater in the molten tin bath.

To one side of the heating chamber, a returning line that connects themolten tin bath and the heating chamber is connected.

It is preferable that the returning line is provided at a deep tindepth, for example, at a position where the depth is in the range of 70to 100 mm and the temperature of the molten tin in the molten tin bathis in the range of 1200 to 1400° C., but the position thereof is notlimited thereto as long as it does not obstruct a flow of molten tin inthe molten tin bath.

As described above, according to the present invention, oxygen in themolten tin is efficiently removed by a difference in oxygen solubilityaccording to the temperature and bubbling of the oxygen stripping gasincluding hydrogen, such that the dissolved oxygen amount of molten tinin the molten tin bath is reduced to several ppm or less, therebylowering product defects.

The invention claimed is:
 1. An apparatus for manufacturing a floatglass by floating the glass on a molten tin that is contained in amolten tin bath, the apparatus comprising: a molten tin bath; adischarge line that is connected to a downstream zone of the molten tinbath, and discharges a portion of the molten tin in the molten tin bathto the outside of the molten tin bath; a stripping chamber including anoxygen stripping chamber that is connected to the discharge line andreceives the molten tin discharged from the molten tin bath through thedischarge line and a heating chamber integrally combined with thestripping chamber, and the stripping chamber being spatially divided toform the oxygen stripping chamber and the heating chamber by a partitionhaving a through hole to transfer the molten tin from which oxygen isremoved in the oxygen stripping chamber into the heating chamber; abubbling device including a porous plate that is provided in the oxygenstripping chamber and bubbles the oxygen stripping gas includinghydrogen through the porous plate into the molten tin in the oxygenstripping chamber; and a returning line that returns the molten tin fromwhich oxygen is removed by the bubbling device to an upstream of themolten tin bath.
 2. The apparatus for manufacturing a float glass as setforth in claim 1, wherein the bubbling device bubbles the oxygenstripping gas including hydrogen in the portion of the molten tinreceived in the oxygen stripping chamber so that a saturation solubilityof oxygen dissolved in the portion of the molten tin is reduced bylowering the temperature of the portion of the molten tin in the oxygenstripping chamber to remove oxygen dissolved in the portion of themolten tin.
 3. The apparatus for manufacturing a float glass as setforth in claim 2, wherein the bubbling device supplies the oxygenstripping gas at a flow rate in the range of 0.2 to 2 Nm³/hr, a pressurein the range of 2 to 5 kgf/cm², and a temperature in the range of 300 to500° C.
 4. The apparatus for manufacturing a float glass as set forth inclaim 2, wherein the oxygen stripping gas further includes an inert gas.5. The apparatus for manufacturing a float glass as set forth in claim4, wherein a mixing ratio of the inert gas and the hydrogen gas of theoxygen stripping gas is 90 or more and less than 100:more than 0 and 10or less on the basis of the volume.
 6. The apparatus for manufacturing afloat glass as set forth in claim 2, further comprising: a gas supplyline that is connected to the oxygen stripping chamber, and supplies theoxygen stripping gas that is bubbled by the bubbling device to theinside of the oxygen stripping chamber.
 7. The apparatus formanufacturing a float glass as set forth in claim 2, wherein thetemperature of the molten tin in the oxygen stripping chamber bubbled bythe bubbling device is in the range of 400 to 700° C.
 8. The apparatusfor manufacturing a float glass as set forth in claim 1, wherein theporous plate has a plurality of holes.
 9. The apparatus formanufacturing a float glass as set forth in claim 8, wherein the holesare inclined with respect to a flat surface of the porous plate.
 10. Theapparatus for manufacturing a float glass as set forth in claim 8,wherein the porous plate is made of a ceramic material.
 11. Theapparatus for manufacturing a float glass as set forth in claim 1,wherein in the oxygen stripping chamber, water (H₂O) is produced byreacting oxygen that is included in the molten tin and hydrogen witheach other, such that oxygen dissolved in the molten tin is removed. 12.The apparatus for manufacturing a float glass as set forth in claim 11,wherein in the oxygen stripping chamber, a discharge outlet throughwhich water (H₂O) is discharged in a steam form to the outside of theoxygen stripping chamber.
 13. The apparatus for manufacturing a floatglass as set forth in claim 1, wherein the temperature of the molten tinheated in the heating chamber is in the range of 1200 to 1400° C. 14.The apparatus for manufacturing a float glass as set forth in claim 1,wherein the through hole is disposed at a position that is lower than aliquid level of the molten tin received in the oxygen stripping chamber.